The present invention relates to the recovery of production fluids from an oil or gas well having a Christmas tree.
Christmas trees are well known in the art of oil and gas wells, and generally comprise an assembly of pipes, valves and fittings installed in a wellhead after completion of drilling and installation of the production tubing to control the flow of oil and gas from the well. Subsea Christmas trees typically have at least two bores one of which communicates with the production tubing (the production bore), and the other of which communicates with the annulus (the annulus bore). The annulus bore and production bore are typically side by side, but various different designs of Christmas tree have different configurations (i.e. concentric bores, side by side bores, and more than two bores etc).
Typical designs of Christmas tree have a side outlet to the production bore closed by a production wing valve for removal of production fluids from the production bore. The top of the production bore and the top of the annulus bore are usually capped by a Christmas tree cap which typically seals off the various bores in the Christmas tree.
Mature sub-sea oil wells producing at high water-cuts often lack the necessary pressure drive to flow at economic rates and are often hampered by the back-pressure exerted on them by the processing facilities. Several means of artificial lift are available to boost production rates, but they either involve a well intervention or modification to the sea bed facilities, both of which are expensive options and may be sub-economic for sub sea wells late in the life cycle with limited remaining reserves.
PCT/GB00/01785 (which is hereby incorporated by reference) describes a method of recovering production fluids from a well having a tree having a first flowpath and a second flowpath, the method comprising diverting fluids from a first portion of the first flowpath to the second flowpath, and diverting the fluids from the second flowpath back to a second portion of the first flowpath, and thereafter recovering fluids from the outlet of the first flowpath, and typically uses a tree cap to seal off the production and annulus bores, and to divert the fluids.
The present invention provides a flow diverter assembly for a tree, the flow diverter assembly having a flow diverter to divert fluids flowing through the production bore of the tree from a first portion of the production bore to the cap, and to divert the fluids back from the cap to a second portion of the production bore for recovery therefrom via an outlet, wherein the flow diverter is detachable from the cap to enable insertion of the flow diverter through the cap.
The tree is typically a subsea tree (such as a Christmas tree) on a subsea well.
The diverter assembly typically includes the cap. The diverter can be locked to the cap by a locking means.
Typically, the diverter assembly can be formed from high-grade steels or other metals, using e.g. resilient or inflatable sealing means as required.
The diverter may include outlets for diversion of the fluids to a pump or treatment assembly remote from the cap.
The flow diverter preferably comprises a conduit capable of insertion into the production bore, the assembly having sealing means capable of sealing the conduit against the wall of the production bore. The conduit may provide a flow diverter through its central bore which typically leads to a tree cap and the pump mentioned previously. The seal effected between the conduit and the production bore prevents fluid from the first portion of the production bore entering the annulus between the conduit and the production bore except as described hereinafter. After passing through a typical booster pump, squeeze or scale chemical treatment apparatus, the fluid is diverted into the second portion of the production bore and from there to the production bore outlet.
Optionally the fluid may be diverted through a crossover back to the production bore and then onto the production bore outlet.
The pump can be powered by high-pressure water or by electricity, which can be supplied direct from a fixed or floating offshore installation, or from a tethered buoy arrangement, or by high-pressure gas from a local source.
The cap preferably seals within Christmas tree bores above an upper master valve. Seals between the cap and bores of the tree are optionally O-ring, inflatable, or preferably metal-to-metal seals. The apparatus can be retrofitted very cost effectively with no disruption to existing pipework and minimal impact on control systems already in place. Preferably the cap includes equivalent hydraulic fluid conduits for control of tree valves, and which match and co-operate with the conduits or other control elements of the tree to which the cap is being fitted.
The typical design of the flow diverter within the cap can vary with the design of tree, the number, size, and configuration of the diverter channels being matched with the production and annulus bores, and others as the case may be. Preferably the diverters in the cap comprise a number of valves to control the inflow and outflow of fluids therefrom. This provides a way to isolate the pump from the production bore if needed, and also provides a bypass loop.
Certain embodiments of the apparatus can typically comprise a conduit that seals within the tree bore above the upper master valve and diverts flow to a remote device for pressure boosting or flow testing. Having flow tested or pressure boosted the produced fluids, the fluids are connected to the annular space between the flow diverter and the original tree bore or the tree crossover pipework/annulus bore, into the existing flowline via the existing wing valve. The concept allows the device to be installed/retro fitted very cost-effectively with no disruption to existing pipework and minimal impact on control systems.
Certain embodiments of the diverter allow insertion through the tree cap after the cap is attached to the tree, and may withdrawn through the cap without detaching the cap from the tree.
Typically the cap is deployed as part of the standard drilling stack. Typically the conduit is fitted to the cap after installation of the cap along with a lower riser package and can use the hydraulic functionality of the existing tree cap to enable additional valves to be controlled, and provides a means to isolate the pump from the production bore, if required. However, certain embodiments of the invention can be deployed without MODU, DSV, or RSV support, can simply be operated from a local tool placed on or near to the tree cap.
The invention also provides a method of installing a flow diverter on a tree, the method comprising attaching a cap to the tree, and installing the diverter through the cap after the cap has been attached to the tree.
The diverter can be carried by the cap (for example on the outboard end of the cap) while the inboard end of the cap is being attached to the tree, or can be conveyed from a remote position (e.g. the surface) after the cap has been attached to the tree.
The conduit is typically attached to the cap, held within the production bore of the tree and sealed therein thus enabling flow to be diverted through the bore of the insert to the cap and thereafter to the surface for testing or pumping then re-injected via the riser annulus or the external flowline through the annulus between the production bore and conduit and into the production pipeline or flowline. Alternatively the fluid may be re-injected into the tree via an annulus or other bore of the tree after treatment, and from there diverted via a crossover to the first flowpath and the outlet.
The flow diverter assembly can be used as part of the drilling riser package to enable flow to be directed through the surface test package, either choke manifold or multiphase meter, and then into the flowline via the tree.
The cap is typically installed on top of the tree and below the Lower Riser Package or the Subsea test tree, dependent on the tree configuration, or as extended tubing from the surface at the surface tree or on coiled tubing or wireline or seal directly against the bore of diverter unit.
The cap typically comprises a connector to interface with the tree, internal valving and flow paths.
The upper end of the conduit may be sealed against the LRP bore at the LRP XOV valve to provide the same function. The upper end of the conduit may be sealed against the surface tree bore to provide the same functionality.
In well test applications, the method enables the produced fluids to be well tested at surface and re-injected into the flowline thus potentially eliminating well flaring and enabling extended well testing.
Following well tests the cap and diverting means can be left in place and connected to a pumping package for pressure boosting if required.
With an MODU, installation of the diverter may be achieved without retrieving and re-running the drilling stack to seabed. With a DSV, the insert removes the need for storage, which brings realistic well testing objectives within the capabilities of a suitably equipped mono hull.
The assembly and method are typically suited for subsea production wells in normal mode or during well testing, but can also be used in subsea water injection wells, land based oil production injection wells, and geothermal wells.
The present invention also provides a method of recovering production fluids from a well having a tree, the tree having a first flowpath and a second flowpath, the method comprising diverting fluids from a first portion of the first flowpath to the second flowpath, and diverting the fluids from the second flowpath back to a second portion of the first flowpath, and thereafter recovering fluids from the outlet of the first flowpath, wherein the fluids are diverted from the wellhead to a remote location, and are returned to the wellhead from the remote location for diversion into the outlet of the first flowpath.
Preferably the first flowpath is a production bore, and the first portion of it is typically a lower part near to the wellhead. The second portion of the first flowpath is typically an upper portion of the bore adjacent a branch outlet, although the second portion can be in the branch or outlet of the first flowpath.
The diversion of fluids from the first flowpath allows the treatment of the fluids (e.g. with chemicals) or pressure boosting for more efficient recovery before re-entry into the first flowpath.
Optionally the second flowpath is an annulus bore of the tree, or an annulus between a conduit inserted into the first flowpath, and the bore of the first flowpath. Other types of bore may optionally be used for the second flowpath instead of an annulus bore.
Typically the flow diversion from the first flowpath to the second flowpath is achieved by a cap on the tree. Optionally, the cap contains a pump or treatment apparatus, but this can preferably be provided separately, or in another part of the apparatus, and in most embodiments, flow will be diverted via the cap to a remote pump etc and returned to the cap by way of tubing.
According to a further aspect of the present invention there is provided a method for recovering fluids from a well having a tree, the tree having a cap and a first flowpath and a second flowpath, the method comprising attaching the cap to the tree, inserting a fluid diverter to divert fluids from a bore of the tree to a second flowpath, diverting fluids from the second flowpath back to a second portion of the bore, and thereafter recovering fluids from the outlet of the bore wherein the first or second flowpath is attached to or detached from the cap without detaching the cap from the tree.
Typically the method includes the step of withdrawing a plug from the bore (e.g. the production bore of the tree) after the cap has bean attached, and thereafter inserting the fluid diverter into the production bore of the tree, typically through the cap.
Preferably the diverter comprises a tubular or other conduit inserted into the production bore. The second flowpath can comprise the bore of the tubular or other conduit. Alternatively the second flowpath may comprise the annulus between the tubular or conduit and a bore (e.g. the production bore) of the tree.
Typically the cap is provided to hold the tubular or other conduit in place. Typically the cap has a through-bore. Optionally the through-bore of the cap has wireline grooves that can engage the conduit, in order to hold it in place in the first flowpath. Alternatively the cap and conduit may engage by other means e.g. resilient teeth, thread etc. Typically the cap is attached to the top of the tree and is inserted as part of the drilling stack (which connects the tree to the surface vessel). The first flowpath is then free from obstructions, and plugs (which are commonly inserted downhole above the production bore outlet before production is commenced) may then be removed. The bore is then typically filled with dense fluid and optionally pressurised in order to prevent well blow out. The conduit is then typically lowered on a line (e.g. wireline) down the drilling stack into the cap, which engages the conduit by the wireline grooves or threads, or by other engaging means as provided. The conduit is then held within the first flowpath.
The conduit typically has a second sealing means, which seals the conduit to the production bore and diverts fluids from a first portion of the production bore into the bore of the second flowpath, normally the annulus.
Embodiments of the invention allow for production fluid or water injection boosting, subsea metering, chemical injection, and extended well test re-injection. For example, in certain embodiments used in a water injection tree, the flow of fluids through the production conduits can be reversed, with water being injected back through the production wing, through the insert and the cap, and into the production bore to pressurise the reservoir.